<div dir="ltr"><div class="gmail_quote"><div dir="ltr" class="gmail_attr">On Fri, Apr 12, 2019 at 6:46 PM Alyssa Rosenzweig <<a href="mailto:alyssa@rosenzweig.io">alyssa@rosenzweig.io</a>> wrote: </div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex">On Mali hardware (supported by Panfrost and Lima), the fixed-function transformation from world-space to screen-space coordinates is done in the vertex shader prior to writing out the gl_Position varying, rather than in dedicated hardware. This commit adds a shared NIR pass for implementing coordinate transformation and lowering gl_Position writes into screen-space gl_Position writes. v2: Run directly on derefs before io/vars are lowered to cleanup the code substantially. Thank you to Qiang for this suggestion! v3: Bikeshed continues. Signed-off-by: Alyssa Rosenzweig <<a href="mailto:alyssa@rosenzweig.io" target="_blank">alyssa@rosenzweig.io</a>> Suggested-by: Qiang Yu <<a href="mailto:yuq825@gmail.com" target="_blank">yuq825@gmail.com</a>> Cc: Jason Ekstrand <<a href="mailto:jason@jlekstrand.net" target="_blank">jason@jlekstrand.net</a>> Cc: Eric Anholt <<a href="mailto:eric@anholt.net" target="_blank">eric@anholt.net</a>> --- src/compiler/nir/meson.build | 1 + src/compiler/nir/nir.h | 1 + .../nir/nir_lower_viewport_transform.c | 101 ++++++++++++++++++ </blockquote><div> </div><div>For some short period of time, we still build with autotools. Please add this to Makefile.sources. That's also required for Android (which may actually be applicable for Mali) </div><div> </div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"> 3 files changed, 103 insertions(+) create mode 100644 src/compiler/nir/nir_lower_viewport_transform.c diff --git a/src/compiler/nir/meson.build b/src/compiler/nir/meson.build index c65f2ff62ff..c274361bdc4 100644 --- a/src/compiler/nir/meson.build +++ b/src/compiler/nir/meson.build @@ -151,6 +151,7 @@ files_libnir = files( 'nir_lower_vars_to_ssa.c', 'nir_lower_var_copies.c', 'nir_lower_vec_to_movs.c', + 'nir_lower_viewport_transform.c', 'nir_lower_wpos_center.c', 'nir_lower_wpos_ytransform.c', 'nir_lower_bit_size.c', diff --git a/src/compiler/nir/nir.h b/src/compiler/nir/nir.h index bc72d8f83f5..0f6ed734efa 100644 --- a/src/compiler/nir/nir.h +++ b/src/compiler/nir/nir.h @@ -3124,6 +3124,7 @@ void nir_lower_io_to_scalar(nir_shader *shader, nir_variable_mode mask); void nir_lower_io_to_scalar_early(nir_shader *shader, nir_variable_mode mask); bool nir_lower_io_to_vector(nir_shader *shader, nir_variable_mode mask); +void nir_lower_viewport_transform(nir_shader *shader); bool nir_lower_uniforms_to_ubo(nir_shader *shader, int multiplier); typedef struct nir_lower_subgroups_options { diff --git a/src/compiler/nir/nir_lower_viewport_transform.c b/src/compiler/nir/nir_lower_viewport_transform.c new file mode 100644 index 00000000000..66085b8da5a --- /dev/null +++ b/src/compiler/nir/nir_lower_viewport_transform.c @@ -0,0 +1,101 @@ +/* + * Copyright (C) 2019 Alyssa Rosenzweig + * + * Permission is hereby granted, free of charge, to any person obtaining a + * copy of this software and associated documentation files (the "Software"), + * to deal in the Software without restriction, including without limitation + * the rights to use, copy, modify, merge, publish, distribute, sublicense, + * and/or sell copies of the Software, and to permit persons to whom the + * Software is furnished to do so, subject to the following conditions: + * + * The above copyright notice and this permission notice (including the next + * paragraph) shall be included in all copies or substantial portions of the + * Software. + * + * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR + * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, + * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL + * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER + * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING + * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS + * IN THE SOFTWARE. + */ + +/* On some hardware (particularly, all current versions of Mali GPUs), + * vertex shaders do not output gl_Position in world-space. Instead, they + * output gl_Position in transformed screen space via the "pseudo" + * position varying. Thus, this pass finds writes to gl_Position and + * changes them to transformed writes, still to gl_Position. The + * outputted screen space is still written back to VARYING_SLOT_POS, + * which is semantically ambiguous but nevertheless a good match for + * Gallium/NIR/Mali. + * + * Implements coordinate transformation as defined in section 12.5 + * "Coordinate Transformation" of the OpenGL ES 3.2 full specification. + * + * This pass must run before lower_vars/lower_io such that derefs are + * still in place. + */ + +#include "nir/nir.h" +#include "nir/nir_builder.h" + +void +nir_lower_viewport_transform(nir_shader *shader) +{ + assert(shader->info.stage == MESA_SHADER_VERTEX); + + nir_foreach_function(func, shader) { + nir_foreach_block(block, func->impl) { + nir_foreach_instr_safe(instr, block) { + if (instr->type != nir_instr_type_intrinsic) + continue; + + nir_intrinsic_instr *intr = nir_instr_as_intrinsic(instr); + if (intr->intrinsic != nir_intrinsic_store_deref) + continue; + + nir_variable *var = nir_intrinsic_get_var(intr, 0); + if (var->data.location != VARYING_SLOT_POS) + continue; + + nir_builder b; + nir_builder_init(&b, func->impl); + b.cursor = nir_before_instr(instr); + + /* Grab the source and viewport */ + nir_ssa_def *input_point = nir_ssa_for_src(&b, intr->src[1], 4); + nir_ssa_def *scale = nir_load_viewport_scale(&b); + nir_ssa_def *offset = nir_load_viewport_offset(&b); + + /* World space to normalised device coordinates to screen space */ + + nir_ssa_def *w_recip = nir_frcp(&b, nir_channel(&b, input_point, 3)); + + nir_ssa_def *ndc_point = nir_fmul(&b, + nir_channels(&b, input_point, 0x7), w_recip); + + nir_ssa_def *screen = nir_fadd(&b, + nir_fmul(&b, ndc_point, scale), offset); + + /* gl_Position will be written out in screenspace xyz, with w set to + * the reciprocal we computed earlier. The transformed w component is + * then used for perspective-correct varying interpolation. The + * transformed w component must preserve its original sign; this is + * used in depth clipping computations */ + + nir_ssa_def *screen_space = nir_vec4(&b, + nir_channel(&b, screen, 0), + nir_channel(&b, screen, 1), + nir_channel(&b, screen, 2), + w_recip); + + nir_instr_rewrite_src(instr, &intr->src[1], + nir_src_for_ssa(screen_space)); + } + } + + nir_metadata_preserve(func->impl, nir_metadata_block_index | + nir_metadata_dominance); + } +} -- 2.20.1 </blockquote></div></div>